Traditionally, electronic displays, such as liquid crystal displays, have been made by sandwiching an optoelectrically active display material between two pieces of glass. In many cases each piece of glass has an etched, clear electrode structure formed using indium tin oxide.
A first electrode structure controls all the segments of the display that may be addressed, that is, changed from one visual state to another. A second electrode, sometimes called a counter electrode, addresses all display segments as one large electrode, and is generally designed without overlap of any rear electrode wire connections that are not desired to affect the image. Alternatively, the second electrode is also patterned to control specific segments of the displays. Unaddressed areas of a display typically have a defined, fixed appearance.
Electrophoretic display media have shown promise for the production displays having lower cost, and displays having lower power consumption. Electrophoretic display media, generally characterized by the movement of particles in an applied electric field, are highly reflective, potentially bistable, and consume very little power. Lateral migration of components of an electrophoretic medium, for example, particles in a fluid, can impair the performance of a display. Hence, an electrophoretic display medium can benefit from inclusion of physical barriers to lateral motion of particles.
Physical barriers, however, present a new problem, because the barrier material typically is unresponsive to addressing of display elements. In effect, a portion of the display surface, as viewed by a user of the display, has a fixed optical characteristic. This effect can, for example, reduce display contrast and brightness.